/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */
package org.apache.tomcat.util.net;

import java.io.EOFException;
import java.io.IOException;
import java.net.SocketTimeoutException;
import java.nio.ByteBuffer;
import java.nio.channels.CompletionHandler;
import java.nio.channels.InterruptedByTimeoutException;
import java.nio.channels.ReadPendingException;
import java.nio.channels.WritePendingException;
import java.util.concurrent.Executor;
import java.util.concurrent.RejectedExecutionException;
import java.util.concurrent.Semaphore;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock.WriteLock;

import org.apache.juli.logging.Log;
import org.apache.juli.logging.LogFactory;
import org.apache.tomcat.util.ExceptionUtils;
import org.apache.tomcat.util.res.StringManager;

public abstract class SocketWrapperBase<E> {

    private static final Log log = LogFactory.getLog(SocketWrapperBase.class);

    protected static final StringManager sm = StringManager.getManager(SocketWrapperBase.class);

    private E socket;
    private final AbstractEndpoint<E,?> endpoint;

    protected final AtomicBoolean closed = new AtomicBoolean(false);

    // Volatile because I/O and setting the timeout values occurs on a different
    // thread to the thread checking the timeout.
    private volatile long readTimeout = -1;
    private volatile long writeTimeout = -1;

    private volatile int keepAliveLeft = 100;
    private volatile boolean upgraded = false;
    private boolean secure = false;
    private String negotiatedProtocol = null;
    /*
     * Following cached for speed / reduced GC
     */
    protected String localAddr = null;
    protected String localName = null;
    protected int localPort = -1;
    protected String remoteAddr = null;
    protected String remoteHost = null;
    protected int remotePort = -1;
    /*
     * Used if block/non-blocking is set at the socket level. The client is
     * responsible for the thread-safe use of this field via the locks provided.
     */
    private volatile boolean blockingStatus = true;
    private final Lock blockingStatusReadLock;
    private final WriteLock blockingStatusWriteLock;
    /*
     * Used to record the first IOException that occurs during non-blocking
     * read/writes that can't be usefully propagated up the stack since there is
     * no user code or appropriate container code in the stack to handle it.
     */
    private volatile IOException error = null;

    
The buffers used for communicating with the socket.
/**
     * The buffers used for communicating with the socket.
     */
    protected volatile SocketBufferHandler socketBufferHandler = null;

    
The max size of the individual buffered write buffers
/**
     * The max size of the individual buffered write buffers
     */
    protected int bufferedWriteSize = 64 * 1024; // 64k default write buffer

    
Additional buffer used for non-blocking writes. Non-blocking writes need
to return immediately even if the data cannot be written immediately but
the socket buffer may not be big enough to hold all of the unwritten
data. This structure provides an additional buffer to hold the data until
it can be written.
Not that while the Servlet API only allows one non-blocking write at a
time, due to buffering and the possible need to write HTTP headers, this
layer may see multiple writes.
/**
     * Additional buffer used for non-blocking writes. Non-blocking writes need
     * to return immediately even if the data cannot be written immediately but
     * the socket buffer may not be big enough to hold all of the unwritten
     * data. This structure provides an additional buffer to hold the data until
     * it can be written.
     * Not that while the Servlet API only allows one non-blocking write at a
     * time, due to buffering and the possible need to write HTTP headers, this
     * layer may see multiple writes.
     */
    protected final WriteBuffer nonBlockingWriteBuffer = new WriteBuffer(bufferedWriteSize);

    protected final Semaphore readPending;
    protected volatile OperationState<?> readOperation = null;
    protected final Semaphore writePending;
    protected volatile OperationState<?> writeOperation = null;

    public SocketWrapperBase(E socket, AbstractEndpoint<E,?> endpoint) {
        this.socket = socket;
        this.endpoint = endpoint;
        ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
        this.blockingStatusReadLock = lock.readLock();
        this.blockingStatusWriteLock = lock.writeLock();
        if (endpoint.getUseAsyncIO() || needSemaphores()) {
            readPending = new Semaphore(1);
            writePending = new Semaphore(1);
        } else {
            readPending = null;
            writePending = null;
        }
    }

    public E getSocket() {
        return socket;
    }

    protected void reset(E closedSocket) {
        socket = closedSocket;
    }

    protected AbstractEndpoint<E,?> getEndpoint() {
        return endpoint;
    }

    
Transfers processing to a container thread.
Params:
runnable – The actions to process on a container thread
Throws:
RejectedExecutionException – If the runnable cannot be executed/**
     * Transfers processing to a container thread.
     *
     * @param runnable The actions to process on a container thread
     *
     * @throws RejectedExecutionException If the runnable cannot be executed
     */
    public void execute(Runnable runnable) {
        Executor executor = endpoint.getExecutor();
        if (!endpoint.isRunning() || executor == null) {
            throw new RejectedExecutionException();
        }
        executor.execute(runnable);
    }

    public IOException getError() { return error; }
    public void setError(IOException error) {
        // Not perfectly thread-safe but good enough. Just needs to ensure that
        // once this.error is non-null, it can never be null.
        if (this.error != null) {
            return;
        }
        this.error = error;
    }
    public void checkError() throws IOException {
        if (error != null) {
            throw error;
        }
    }

    public boolean isUpgraded() { return upgraded; }
    public void setUpgraded(boolean upgraded) { this.upgraded = upgraded; }
    public boolean isSecure() { return secure; }
    public void setSecure(boolean secure) { this.secure = secure; }
    public String getNegotiatedProtocol() { return negotiatedProtocol; }
    public void setNegotiatedProtocol(String negotiatedProtocol) {
        this.negotiatedProtocol = negotiatedProtocol;
    }

    
Set the timeout for reading. Values of zero or less will be changed to
-1.
Params:
readTimeout – The timeout in milliseconds. A value of -1 indicates
                   an infinite timeout./**
     * Set the timeout for reading. Values of zero or less will be changed to
     * -1.
     *
     * @param readTimeout The timeout in milliseconds. A value of -1 indicates
     *                    an infinite timeout.
     */
    public void setReadTimeout(long readTimeout) {
        if (readTimeout > 0) {
            this.readTimeout = readTimeout;
        } else {
            this.readTimeout = -1;
        }
    }

    public long getReadTimeout() {
        return this.readTimeout;
    }

    
Set the timeout for writing. Values of zero or less will be changed to
-1.
Params:
writeTimeout – The timeout in milliseconds. A value of zero or less
                   indicates an infinite timeout./**
     * Set the timeout for writing. Values of zero or less will be changed to
     * -1.
     *
     * @param writeTimeout The timeout in milliseconds. A value of zero or less
     *                    indicates an infinite timeout.
     */
    public void setWriteTimeout(long writeTimeout) {
        if (writeTimeout > 0) {
            this.writeTimeout = writeTimeout;
        } else {
            this.writeTimeout = -1;
        }
    }

    public long getWriteTimeout() {
        return this.writeTimeout;
    }

    public void setKeepAliveLeft(int keepAliveLeft) {
        this.keepAliveLeft = keepAliveLeft;
    }

    public int decrementKeepAlive() {
        return --keepAliveLeft;
    }

    public String getRemoteHost() {
        if (remoteHost == null) {
            populateRemoteHost();
        }
        return remoteHost;
    }
    protected abstract void populateRemoteHost();

    public String getRemoteAddr() {
        if (remoteAddr == null) {
            populateRemoteAddr();
        }
        return remoteAddr;
    }
    protected abstract void populateRemoteAddr();

    public int getRemotePort() {
        if (remotePort == -1) {
            populateRemotePort();
        }
        return remotePort;
    }
    protected abstract void populateRemotePort();

    public String getLocalName() {
        if (localName == null) {
            populateLocalName();
        }
        return localName;
    }
    protected abstract void populateLocalName();

    public String getLocalAddr() {
        if (localAddr == null) {
            populateLocalAddr();
        }
        return localAddr;
    }
    protected abstract void populateLocalAddr();

    public int getLocalPort() {
        if (localPort == -1) {
            populateLocalPort();
        }
        return localPort;
    }
    protected abstract void populateLocalPort();

    public boolean getBlockingStatus() { return blockingStatus; }
    public void setBlockingStatus(boolean blockingStatus) {
        this.blockingStatus = blockingStatus;
    }
    public Lock getBlockingStatusReadLock() { return blockingStatusReadLock; }
    public WriteLock getBlockingStatusWriteLock() {
        return blockingStatusWriteLock;
    }
    public SocketBufferHandler getSocketBufferHandler() { return socketBufferHandler; }

    public boolean hasDataToRead() {
        // Return true because it is always safe to make a read attempt
        return true;
    }

    public boolean hasDataToWrite() {
        return !socketBufferHandler.isWriteBufferEmpty() || !nonBlockingWriteBuffer.isEmpty();
    }

    
Checks to see if there are any writes pending and if there are calls registerWriteInterest() to trigger a callback once the pending writes have completed. 

Note: Once this method has returned false it MUST NOT be called again until the pending write has completed and the callback has been fired. TODO: Modify registerWriteInterest() so the above restriction is enforced there rather than relying on the caller. 
Returns:
true if no writes are pending and data can be
        written otherwise false/**
     * Checks to see if there are any writes pending and if there are calls
     * {@link #registerWriteInterest()} to trigger a callback once the pending
     * writes have completed.
     * <p>
     * Note: Once this method has returned <code>false</code> it <b>MUST NOT</b>
     *       be called again until the pending write has completed and the
     *       callback has been fired.
     *       TODO: Modify {@link #registerWriteInterest()} so the above
     *       restriction is enforced there rather than relying on the caller.
     *
     * @return <code>true</code> if no writes are pending and data can be
     *         written otherwise <code>false</code>
     */
    public boolean isReadyForWrite() {
        boolean result = canWrite();
        if (!result) {
            registerWriteInterest();
        }
        return result;
    }


    public boolean canWrite() {
        if (socketBufferHandler == null) {
            throw new IllegalStateException(sm.getString("socket.closed"));
        }
        return socketBufferHandler.isWriteBufferWritable() && nonBlockingWriteBuffer.isEmpty();
    }


    
Overridden for debug purposes. No guarantees are made about the format of
this message which may vary significantly between point releases.

{@inheritDoc}
/**
     * Overridden for debug purposes. No guarantees are made about the format of
     * this message which may vary significantly between point releases.
     * <p>
     * {@inheritDoc}
     */
    @Override
    public String toString() {
        return super.toString() + ":" + String.valueOf(socket);
    }


    public abstract int read(boolean block, byte[] b, int off, int len) throws IOException;
    public abstract int read(boolean block, ByteBuffer to) throws IOException;
    public abstract boolean isReadyForRead() throws IOException;
    public abstract void setAppReadBufHandler(ApplicationBufferHandler handler);

    protected int populateReadBuffer(byte[] b, int off, int len) {
        socketBufferHandler.configureReadBufferForRead();
        ByteBuffer readBuffer = socketBufferHandler.getReadBuffer();
        int remaining = readBuffer.remaining();

        // Is there enough data in the read buffer to satisfy this request?
        // Copy what data there is in the read buffer to the byte array
        if (remaining > 0) {
            remaining = Math.min(remaining, len);
            readBuffer.get(b, off, remaining);

            if (log.isDebugEnabled()) {
                log.debug("Socket: [" + this + "], Read from buffer: [" + remaining + "]");
            }
        }
        return remaining;
    }


    protected int populateReadBuffer(ByteBuffer to) {
        // Is there enough data in the read buffer to satisfy this request?
        // Copy what data there is in the read buffer to the byte array
        socketBufferHandler.configureReadBufferForRead();
        int nRead = transfer(socketBufferHandler.getReadBuffer(), to);

        if (log.isDebugEnabled()) {
            log.debug("Socket: [" + this + "], Read from buffer: [" + nRead + "]");
        }
        return nRead;
    }


    
Return input that has been read to the input buffer for re-reading by the
correct component. There are times when a component may read more data
than it needs before it passes control to another component. One example
of this is during HTTP upgrade. If an (arguably misbehaving client) sends
data associated with the upgraded protocol before the HTTP upgrade
completes, the HTTP handler may read it. This method provides a way for
that data to be returned so it can be processed by the correct component.
Params:
returnedInput – The input to return to the input buffer./**
     * Return input that has been read to the input buffer for re-reading by the
     * correct component. There are times when a component may read more data
     * than it needs before it passes control to another component. One example
     * of this is during HTTP upgrade. If an (arguably misbehaving client) sends
     * data associated with the upgraded protocol before the HTTP upgrade
     * completes, the HTTP handler may read it. This method provides a way for
     * that data to be returned so it can be processed by the correct component.
     *
     * @param returnedInput The input to return to the input buffer.
     */
    public void unRead(ByteBuffer returnedInput) {
        if (returnedInput != null) {
            socketBufferHandler.configureReadBufferForWrite();
            socketBufferHandler.getReadBuffer().put(returnedInput);
        }
    }


    
Close the socket wrapper.
/**
     * Close the socket wrapper.
     */
    public void close() {
        if (closed.compareAndSet(false, true)) {
            doClose();
        }
    }

    
Perform the actual close. The closed atomic boolean guarantees this will
be called only once per wrapper.
/**
     * Perform the actual close. The closed atomic boolean guarantees this will
     * be called only once per wrapper.
     */
    protected abstract void doClose();

    
Returns:
true if the wrapper has been closed/**
     * @return true if the wrapper has been closed
     */
    public boolean isClosed() {
        return closed.get();
    }


    
Writes the provided data to the socket write buffer. If the socket write
buffer fills during the write, the content of the socket write buffer is
written to the network and this method starts to fill the socket write
buffer again. Depending on the size of the data to write, there may be
multiple writes to the network.

Non-blocking writes must return immediately and the byte array holding
the data to be written must be immediately available for re-use. It may
not be possible to write sufficient data to the network to allow this to
happen. In this case data that cannot be written to the network and
cannot be held by the socket buffer is stored in the non-blocking write
buffer.

Note: There is an implementation assumption that, before switching from
      non-blocking writes to blocking writes, any data remaining in the
      non-blocking write buffer will have been written to the network.
Params:
block – true if a blocking write should be used,
                 otherwise a non-blocking write will be used
buf –   The byte array containing the data to be written
off –   The offset within the byte array of the data to be written
len –   The length of the data to be written
Throws:
IOException – If an IO error occurs during the write/**
     * Writes the provided data to the socket write buffer. If the socket write
     * buffer fills during the write, the content of the socket write buffer is
     * written to the network and this method starts to fill the socket write
     * buffer again. Depending on the size of the data to write, there may be
     * multiple writes to the network.
     * <p>
     * Non-blocking writes must return immediately and the byte array holding
     * the data to be written must be immediately available for re-use. It may
     * not be possible to write sufficient data to the network to allow this to
     * happen. In this case data that cannot be written to the network and
     * cannot be held by the socket buffer is stored in the non-blocking write
     * buffer.
     * <p>
     * Note: There is an implementation assumption that, before switching from
     *       non-blocking writes to blocking writes, any data remaining in the
     *       non-blocking write buffer will have been written to the network.
     *
     * @param block <code>true</code> if a blocking write should be used,
     *                  otherwise a non-blocking write will be used
     * @param buf   The byte array containing the data to be written
     * @param off   The offset within the byte array of the data to be written
     * @param len   The length of the data to be written
     *
     * @throws IOException If an IO error occurs during the write
     */
    public final void write(boolean block, byte[] buf, int off, int len) throws IOException {
        if (len == 0 || buf == null) {
            return;
        }

        /*
         * While the implementations for blocking and non-blocking writes are
         * very similar they have been split into separate methods:
         * - To allow sub-classes to override them individually. NIO2, for
         *   example, overrides the non-blocking write but not the blocking
         *   write.
         * - To enable a marginally more efficient implemented for blocking
         *   writes which do not require the additional checks related to the
         *   use of the non-blocking write buffer
         */
        if (block) {
            writeBlocking(buf, off, len);
        } else {
            writeNonBlocking(buf, off, len);
        }
    }


    
Writes the provided data to the socket write buffer. If the socket write
buffer fills during the write, the content of the socket write buffer is
written to the network and this method starts to fill the socket write
buffer again. Depending on the size of the data to write, there may be
multiple writes to the network.

Non-blocking writes must return immediately and the ByteBuffer holding
the data to be written must be immediately available for re-use. It may
not be possible to write sufficient data to the network to allow this to
happen. In this case data that cannot be written to the network and
cannot be held by the socket buffer is stored in the non-blocking write
buffer.

Note: There is an implementation assumption that, before switching from
      non-blocking writes to blocking writes, any data remaining in the
      non-blocking write buffer will have been written to the network.
Params:
block –  true if a blocking write should be used,
              otherwise a non-blocking write will be used
from –   The ByteBuffer containing the data to be written
Throws:
IOException – If an IO error occurs during the write/**
     * Writes the provided data to the socket write buffer. If the socket write
     * buffer fills during the write, the content of the socket write buffer is
     * written to the network and this method starts to fill the socket write
     * buffer again. Depending on the size of the data to write, there may be
     * multiple writes to the network.
     * <p>
     * Non-blocking writes must return immediately and the ByteBuffer holding
     * the data to be written must be immediately available for re-use. It may
     * not be possible to write sufficient data to the network to allow this to
     * happen. In this case data that cannot be written to the network and
     * cannot be held by the socket buffer is stored in the non-blocking write
     * buffer.
     * <p>
     * Note: There is an implementation assumption that, before switching from
     *       non-blocking writes to blocking writes, any data remaining in the
     *       non-blocking write buffer will have been written to the network.
     *
     * @param block  <code>true</code> if a blocking write should be used,
     *               otherwise a non-blocking write will be used
     * @param from   The ByteBuffer containing the data to be written
     *
     * @throws IOException If an IO error occurs during the write
     */
    public final void write(boolean block, ByteBuffer from) throws IOException {
        if (from == null || from.remaining() == 0) {
            return;
        }

        /*
         * While the implementations for blocking and non-blocking writes are
         * very similar they have been split into separate methods:
         * - To allow sub-classes to override them individually. NIO2, for
         *   example, overrides the non-blocking write but not the blocking
         *   write.
         * - To enable a marginally more efficient implemented for blocking
         *   writes which do not require the additional checks related to the
         *   use of the non-blocking write buffer
         */
        if (block) {
            writeBlocking(from);
        } else {
            writeNonBlocking(from);
        }
    }


    
Writes the provided data to the socket write buffer. If the socket write
buffer fills during the write, the content of the socket write buffer is
written to the network using a blocking write. Once that blocking write
is complete, this method starts to fill the socket write buffer again.
Depending on the size of the data to write, there may be multiple writes
to the network. On completion of this method there will always be space
remaining in the socket write buffer.
Params:
buf –   The byte array containing the data to be written
off –   The offset within the byte array of the data to be written
len –   The length of the data to be written
Throws:
IOException – If an IO error occurs during the write/**
     * Writes the provided data to the socket write buffer. If the socket write
     * buffer fills during the write, the content of the socket write buffer is
     * written to the network using a blocking write. Once that blocking write
     * is complete, this method starts to fill the socket write buffer again.
     * Depending on the size of the data to write, there may be multiple writes
     * to the network. On completion of this method there will always be space
     * remaining in the socket write buffer.
     *
     * @param buf   The byte array containing the data to be written
     * @param off   The offset within the byte array of the data to be written
     * @param len   The length of the data to be written
     *
     * @throws IOException If an IO error occurs during the write
     */
    protected void writeBlocking(byte[] buf, int off, int len) throws IOException {
        socketBufferHandler.configureWriteBufferForWrite();
        int thisTime = transfer(buf, off, len, socketBufferHandler.getWriteBuffer());
        while (socketBufferHandler.getWriteBuffer().remaining() == 0) {
            len = len - thisTime;
            off = off + thisTime;
            doWrite(true);
            socketBufferHandler.configureWriteBufferForWrite();
            thisTime = transfer(buf, off, len, socketBufferHandler.getWriteBuffer());
        }
    }


    
Writes the provided data to the socket write buffer. If the socket write
buffer fills during the write, the content of the socket write buffer is
written to the network using a blocking write. Once that blocking write
is complete, this method starts to fill the socket write buffer again.
Depending on the size of the data to write, there may be multiple writes
to the network. On completion of this method there will always be space
remaining in the socket write buffer.
Params:
from – The ByteBuffer containing the data to be written
Throws:
IOException – If an IO error occurs during the write/**
     * Writes the provided data to the socket write buffer. If the socket write
     * buffer fills during the write, the content of the socket write buffer is
     * written to the network using a blocking write. Once that blocking write
     * is complete, this method starts to fill the socket write buffer again.
     * Depending on the size of the data to write, there may be multiple writes
     * to the network. On completion of this method there will always be space
     * remaining in the socket write buffer.
     *
     * @param from The ByteBuffer containing the data to be written
     *
     * @throws IOException If an IO error occurs during the write
     */
    protected void writeBlocking(ByteBuffer from) throws IOException {
        if (socketBufferHandler.isWriteBufferEmpty()) {
            // Socket write buffer is empty. Write the provided buffer directly
            // to the network.
            // TODO Shouldn't smaller writes be buffered anyway?
            writeBlockingDirect(from);
        } else {
            // Socket write buffer has some data.
            socketBufferHandler.configureWriteBufferForWrite();
            // Put as much data as possible into the write buffer
            transfer(from, socketBufferHandler.getWriteBuffer());
            // If the buffer is now full, write it to the network and then write
            // the remaining data directly to the network.
            if (!socketBufferHandler.isWriteBufferWritable()) {
                doWrite(true);
                writeBlockingDirect(from);
            }
        }
    }


    
Writes directly to the network, bypassing the socket write buffer.
Params:
from – The ByteBuffer containing the data to be written
Throws:
IOException – If an IO error occurs during the write/**
     * Writes directly to the network, bypassing the socket write buffer.
     *
     * @param from The ByteBuffer containing the data to be written
     *
     * @throws IOException If an IO error occurs during the write
     */
    protected void writeBlockingDirect(ByteBuffer from) throws IOException {
        // The socket write buffer capacity is socket.appWriteBufSize
        // TODO This only matters when using TLS. For non-TLS connections it
        //      should be possible to write the ByteBuffer in a single write
        int limit = socketBufferHandler.getWriteBuffer().capacity();
        int fromLimit = from.limit();
        while (from.remaining() >= limit) {
            from.limit(from.position() + limit);
            doWrite(true, from);
            from.limit(fromLimit);
        }

        if (from.remaining() > 0) {
            socketBufferHandler.configureWriteBufferForWrite();
            transfer(from, socketBufferHandler.getWriteBuffer());
        }
    }


    
Transfers the data to the socket write buffer (writing that data to the
socket if the buffer fills up using a non-blocking write) until either
all the data has been transferred and space remains in the socket write
buffer or a non-blocking write leaves data in the socket write buffer.
After an incomplete write, any data remaining to be transferred to the
socket write buffer will be copied to the socket write buffer. If the
remaining data is too big for the socket write buffer, the socket write
buffer will be filled and the additional data written to the non-blocking
write buffer.
Params:
buf –   The byte array containing the data to be written
off –   The offset within the byte array of the data to be written
len –   The length of the data to be written
Throws:
IOException – If an IO error occurs during the write/**
     * Transfers the data to the socket write buffer (writing that data to the
     * socket if the buffer fills up using a non-blocking write) until either
     * all the data has been transferred and space remains in the socket write
     * buffer or a non-blocking write leaves data in the socket write buffer.
     * After an incomplete write, any data remaining to be transferred to the
     * socket write buffer will be copied to the socket write buffer. If the
     * remaining data is too big for the socket write buffer, the socket write
     * buffer will be filled and the additional data written to the non-blocking
     * write buffer.
     *
     * @param buf   The byte array containing the data to be written
     * @param off   The offset within the byte array of the data to be written
     * @param len   The length of the data to be written
     *
     * @throws IOException If an IO error occurs during the write
     */
    protected void writeNonBlocking(byte[] buf, int off, int len) throws IOException {
        if (nonBlockingWriteBuffer.isEmpty() && socketBufferHandler.isWriteBufferWritable()) {
            socketBufferHandler.configureWriteBufferForWrite();
            int thisTime = transfer(buf, off, len, socketBufferHandler.getWriteBuffer());
            len = len - thisTime;
            while (!socketBufferHandler.isWriteBufferWritable()) {
                off = off + thisTime;
                doWrite(false);
                if (len > 0 && socketBufferHandler.isWriteBufferWritable()) {
                    socketBufferHandler.configureWriteBufferForWrite();
                    thisTime = transfer(buf, off, len, socketBufferHandler.getWriteBuffer());
                } else {
                    // Didn't write any data in the last non-blocking write.
                    // Therefore the write buffer will still be full. Nothing
                    // else to do here. Exit the loop.
                    break;
                }
                len = len - thisTime;
            }
        }

        if (len > 0) {
            // Remaining data must be buffered
            nonBlockingWriteBuffer.add(buf, off, len);
        }
    }


    
Transfers the data to the socket write buffer (writing that data to the
socket if the buffer fills up using a non-blocking write) until either
all the data has been transferred and space remains in the socket write
buffer or a non-blocking write leaves data in the socket write buffer.
After an incomplete write, any data remaining to be transferred to the
socket write buffer will be copied to the socket write buffer. If the
remaining data is too big for the socket write buffer, the socket write
buffer will be filled and the additional data written to the non-blocking
write buffer.
Params:
from – The ByteBuffer containing the data to be written
Throws:
IOException – If an IO error occurs during the write/**
     * Transfers the data to the socket write buffer (writing that data to the
     * socket if the buffer fills up using a non-blocking write) until either
     * all the data has been transferred and space remains in the socket write
     * buffer or a non-blocking write leaves data in the socket write buffer.
     * After an incomplete write, any data remaining to be transferred to the
     * socket write buffer will be copied to the socket write buffer. If the
     * remaining data is too big for the socket write buffer, the socket write
     * buffer will be filled and the additional data written to the non-blocking
     * write buffer.
     *
     * @param from The ByteBuffer containing the data to be written
     *
     * @throws IOException If an IO error occurs during the write
     */
    protected void writeNonBlocking(ByteBuffer from)
            throws IOException {

        if (nonBlockingWriteBuffer.isEmpty() && socketBufferHandler.isWriteBufferWritable()) {
            writeNonBlockingInternal(from);
        }

        if (from.remaining() > 0) {
            // Remaining data must be buffered
            nonBlockingWriteBuffer.add(from);
        }
    }


    
Separate method so it can be re-used by the socket write buffer to write
data to the network
Params:
from – The ByteBuffer containing the data to be written
Throws:
IOException – If an IO error occurs during the write/**
     * Separate method so it can be re-used by the socket write buffer to write
     * data to the network
     *
     * @param from The ByteBuffer containing the data to be written
     *
     * @throws IOException If an IO error occurs during the write
     */
    protected void writeNonBlockingInternal(ByteBuffer from) throws IOException {
        if (socketBufferHandler.isWriteBufferEmpty()) {
            writeNonBlockingDirect(from);
        } else {
            socketBufferHandler.configureWriteBufferForWrite();
            transfer(from, socketBufferHandler.getWriteBuffer());
            if (!socketBufferHandler.isWriteBufferWritable()) {
                doWrite(false);
                if (socketBufferHandler.isWriteBufferWritable()) {
                    writeNonBlockingDirect(from);
                }
            }
        }
    }


    protected void writeNonBlockingDirect(ByteBuffer from) throws IOException {
        // The socket write buffer capacity is socket.appWriteBufSize
        // TODO This only matters when using TLS. For non-TLS connections it
        //      should be possible to write the ByteBuffer in a single write
        int limit = socketBufferHandler.getWriteBuffer().capacity();
        int fromLimit = from.limit();
        while (from.remaining() >= limit) {
            int newLimit = from.position() + limit;
            from.limit(newLimit);
            doWrite(false, from);
            from.limit(fromLimit);
            if (from.position() != newLimit) {
                // Didn't write the whole amount of data in the last
                // non-blocking write.
                // Exit the loop.
                return;
            }
        }

        if (from.remaining() > 0) {
            socketBufferHandler.configureWriteBufferForWrite();
            transfer(from, socketBufferHandler.getWriteBuffer());
        }
    }


    
Writes as much data as possible from any that remains in the buffers.
Params:
block – true if a blocking write should be used,
                 otherwise a non-blocking write will be used
Throws:
IOException – If an IO error occurs during the write
Returns:
true if data remains to be flushed after this method
        completes, otherwise false. In blocking mode
        therefore, the return value should always be false/**
     * Writes as much data as possible from any that remains in the buffers.
     *
     * @param block <code>true</code> if a blocking write should be used,
     *                  otherwise a non-blocking write will be used
     *
     * @return <code>true</code> if data remains to be flushed after this method
     *         completes, otherwise <code>false</code>. In blocking mode
     *         therefore, the return value should always be <code>false</code>
     *
     * @throws IOException If an IO error occurs during the write
     */
    public boolean flush(boolean block) throws IOException {
        boolean result = false;
        if (block) {
            // A blocking flush will always empty the buffer.
            flushBlocking();
        } else {
            result = flushNonBlocking();
        }

        return result;
    }


    protected void flushBlocking() throws IOException {
        doWrite(true);

        if (!nonBlockingWriteBuffer.isEmpty()) {
            nonBlockingWriteBuffer.write(this, true);

            if (!socketBufferHandler.isWriteBufferEmpty()) {
                doWrite(true);
            }
        }

    }


    protected boolean flushNonBlocking() throws IOException {
        boolean dataLeft = !socketBufferHandler.isWriteBufferEmpty();

        // Write to the socket, if there is anything to write
        if (dataLeft) {
            doWrite(false);
            dataLeft = !socketBufferHandler.isWriteBufferEmpty();
        }

        if (!dataLeft && !nonBlockingWriteBuffer.isEmpty()) {
            dataLeft = nonBlockingWriteBuffer.write(this, false);

            if (!dataLeft && !socketBufferHandler.isWriteBufferEmpty()) {
                doWrite(false);
                dataLeft = !socketBufferHandler.isWriteBufferEmpty();
            }
        }

        return dataLeft;
    }


    
Write the contents of the socketWriteBuffer to the socket. For blocking
writes either then entire contents of the buffer will be written or an
IOException will be thrown. Partial blocking writes will not occur.
Params:
block – Should the write be blocking or not?
Throws:
IOException – If an I/O error such as a timeout occurs during the
                    write/**
     * Write the contents of the socketWriteBuffer to the socket. For blocking
     * writes either then entire contents of the buffer will be written or an
     * IOException will be thrown. Partial blocking writes will not occur.
     *
     * @param block Should the write be blocking or not?
     *
     * @throws IOException If an I/O error such as a timeout occurs during the
     *                     write
     */
    protected void doWrite(boolean block) throws IOException {
        socketBufferHandler.configureWriteBufferForRead();
        doWrite(block, socketBufferHandler.getWriteBuffer());
    }


    
Write the contents of the ByteBuffer to the socket. For blocking writes
either then entire contents of the buffer will be written or an
IOException will be thrown. Partial blocking writes will not occur.
Params:
block – Should the write be blocking or not?
from – the ByteBuffer containing the data to be written
Throws:
IOException – If an I/O error such as a timeout occurs during the
                    write/**
     * Write the contents of the ByteBuffer to the socket. For blocking writes
     * either then entire contents of the buffer will be written or an
     * IOException will be thrown. Partial blocking writes will not occur.
     *
     * @param block Should the write be blocking or not?
     * @param from the ByteBuffer containing the data to be written
     *
     * @throws IOException If an I/O error such as a timeout occurs during the
     *                     write
     */
    protected abstract void doWrite(boolean block, ByteBuffer from) throws IOException;


    public void processSocket(SocketEvent socketStatus, boolean dispatch) {
        endpoint.processSocket(this, socketStatus, dispatch);
    }


    public abstract void registerReadInterest();

    public abstract void registerWriteInterest();

    public abstract SendfileDataBase createSendfileData(String filename, long pos, long length);

    
Starts the sendfile process. It is expected that if the sendfile process
does not complete during this call and does not report an error, that the
caller will not add the socket to the poller (or equivalent). That
is the responsibility of this method.
Params:
sendfileData – Data representing the file to send
Returns:
The state of the sendfile process after the first write./**
     * Starts the sendfile process. It is expected that if the sendfile process
     * does not complete during this call and does not report an error, that the
     * caller <b>will not</b> add the socket to the poller (or equivalent). That
     * is the responsibility of this method.
     *
     * @param sendfileData Data representing the file to send
     *
     * @return The state of the sendfile process after the first write.
     */
    public abstract SendfileState processSendfile(SendfileDataBase sendfileData);

    
Require the client to perform CLIENT-CERT authentication if it hasn't
already done so.
Params:
sslSupport – The SSL/TLS support instance currently being used by
                  the connection that may need updating after the client
                  authentication
Throws:
IOException – If authentication is required then there will be I/O
                    with the client and this exception will be thrown if
                    that goes wrong/**
     * Require the client to perform CLIENT-CERT authentication if it hasn't
     * already done so.
     *
     * @param sslSupport The SSL/TLS support instance currently being used by
     *                   the connection that may need updating after the client
     *                   authentication
     *
     * @throws IOException If authentication is required then there will be I/O
     *                     with the client and this exception will be thrown if
     *                     that goes wrong
     */
    public abstract void doClientAuth(SSLSupport sslSupport) throws IOException;

    public abstract SSLSupport getSslSupport(String clientCertProvider);


    // ------------------------------------------------------- NIO 2 style APIs


    public enum BlockingMode {
        
The operation will not block. If there are pending operations,
the operation will throw a pending exception.
/**
         * The operation will not block. If there are pending operations,
         * the operation will throw a pending exception.
         */
        CLASSIC,
        
The operation will not block. If there are pending operations,
the operation will return CompletionState.NOT_DONE.
/**
         * The operation will not block. If there are pending operations,
         * the operation will return CompletionState.NOT_DONE.
         */
        NON_BLOCK,
        
The operation will block until pending operations are completed, but
will not block after performing it.
/**
         * The operation will block until pending operations are completed, but
         * will not block after performing it.
         */
        SEMI_BLOCK,
        
The operation will block until completed.
/**
         * The operation will block until completed.
         */
        BLOCK
    }

    public enum CompletionState {
        
Operation is still pending.
/**
         * Operation is still pending.
         */
        PENDING,
        
Operation was pending and non blocking.
/**
         * Operation was pending and non blocking.
         */
        NOT_DONE,
        
The operation completed inline.
/**
         * The operation completed inline.
         */
        INLINE,
        
The operation completed inline but failed.
/**
         * The operation completed inline but failed.
         */
        ERROR,
        
The operation completed, but not inline.
/**
         * The operation completed, but not inline.
         */
        DONE
    }

    public enum CompletionHandlerCall {
        
Operation should continue, the completion handler shouldn't be
called.
/**
         * Operation should continue, the completion handler shouldn't be
         * called.
         */
        CONTINUE,
        
The operation completed but the completion handler shouldn't be
called.
/**
         * The operation completed but the completion handler shouldn't be
         * called.
         */
        NONE,
        
The operation is complete, the completion handler should be
called.
/**
         * The operation is complete, the completion handler should be
         * called.
         */
        DONE
    }

    public interface CompletionCheck {
        
Determine what call, if any, should be made to the completion
handler.
Params:
state – of the operation (done or done in-line since the
       IO call is done)
buffers – ByteBuffer[] that has been passed to the
       original IO call
offset – that has been passed to the original IO call
length – that has been passed to the original IO call
Returns:
The call, if any, to make to the completion handler/**
         * Determine what call, if any, should be made to the completion
         * handler.
         *
         * @param state of the operation (done or done in-line since the
         *        IO call is done)
         * @param buffers ByteBuffer[] that has been passed to the
         *        original IO call
         * @param offset that has been passed to the original IO call
         * @param length that has been passed to the original IO call
         *
         * @return The call, if any, to make to the completion handler
         */
        public CompletionHandlerCall callHandler(CompletionState state, ByteBuffer[] buffers,
                int offset, int length);
    }

    
This utility CompletionCheck will cause the write to fully write
all remaining data. If the operation completes inline, the
completion handler will not be called.
/**
     * This utility CompletionCheck will cause the write to fully write
     * all remaining data. If the operation completes inline, the
     * completion handler will not be called.
     */
    public static final CompletionCheck COMPLETE_WRITE = new CompletionCheck() {
        @Override
        public CompletionHandlerCall callHandler(CompletionState state, ByteBuffer[] buffers,
                int offset, int length) {
            for (int i = 0; i < length; i++) {
                if (buffers[offset + i].hasRemaining()) {
                    return CompletionHandlerCall.CONTINUE;
                }
            }
            return (state == CompletionState.DONE) ? CompletionHandlerCall.DONE
                    : CompletionHandlerCall.NONE;
        }
    };

    
This utility CompletionCheck will cause the write to fully write
all remaining data. The completion handler will then be called.
/**
     * This utility CompletionCheck will cause the write to fully write
     * all remaining data. The completion handler will then be called.
     */
    public static final CompletionCheck COMPLETE_WRITE_WITH_COMPLETION = new CompletionCheck() {
        @Override
        public CompletionHandlerCall callHandler(CompletionState state, ByteBuffer[] buffers,
                int offset, int length) {
            for (int i = 0; i < length; i++) {
                if (buffers[offset + i].hasRemaining()) {
                    return CompletionHandlerCall.CONTINUE;
                }
            }
            return CompletionHandlerCall.DONE;
        }
    };

    
This utility CompletionCheck will cause the completion handler
to be called once some data has been read. If the operation
completes inline, the completion handler will not be called.
/**
     * This utility CompletionCheck will cause the completion handler
     * to be called once some data has been read. If the operation
     * completes inline, the completion handler will not be called.
     */
    public static final CompletionCheck READ_DATA = new CompletionCheck() {
        @Override
        public CompletionHandlerCall callHandler(CompletionState state, ByteBuffer[] buffers,
                int offset, int length) {
            return (state == CompletionState.DONE) ? CompletionHandlerCall.DONE
                    : CompletionHandlerCall.NONE;
        }
    };

    
This utility CompletionCheck will cause the completion handler
to be called once the given buffers are full. The completion
handler will then be called.
/**
     * This utility CompletionCheck will cause the completion handler
     * to be called once the given buffers are full. The completion
     * handler will then be called.
     */
    public static final CompletionCheck COMPLETE_READ_WITH_COMPLETION = COMPLETE_WRITE_WITH_COMPLETION;

    
This utility CompletionCheck will cause the completion handler
to be called once the given buffers are full. If the operation
completes inline, the completion handler will not be called.
/**
     * This utility CompletionCheck will cause the completion handler
     * to be called once the given buffers are full. If the operation
     * completes inline, the completion handler will not be called.
     */
    public static final CompletionCheck COMPLETE_READ = COMPLETE_WRITE;

    
Internal state tracker for vectored operations.
/**
     * Internal state tracker for vectored operations.
     */
    protected abstract class OperationState<A> implements Runnable {
        protected final boolean read;
        protected final ByteBuffer[] buffers;
        protected final int offset;
        protected final int length;
        protected final A attachment;
        protected final long timeout;
        protected final TimeUnit unit;
        protected final BlockingMode block;
        protected final CompletionCheck check;
        protected final CompletionHandler<Long, ? super A> handler;
        protected final Semaphore semaphore;
        protected final VectoredIOCompletionHandler<A> completion;
        protected OperationState(boolean read, ByteBuffer[] buffers, int offset, int length,
                BlockingMode block, long timeout, TimeUnit unit, A attachment,
                CompletionCheck check, CompletionHandler<Long, ? super A> handler,
                Semaphore semaphore, VectoredIOCompletionHandler<A> completion) {
            this.read = read;
            this.buffers = buffers;
            this.offset = offset;
            this.length = length;
            this.block = block;
            this.timeout = timeout;
            this.unit = unit;
            this.attachment = attachment;
            this.check = check;
            this.handler = handler;
            this.semaphore = semaphore;
            this.completion = completion;
        }
        protected volatile long nBytes = 0;
        protected volatile CompletionState state = CompletionState.PENDING;
        protected boolean completionDone = true;

        
Returns:
true if the operation is still inline, false if the operation
  is running on a thread that is not the original caller/**
         * @return true if the operation is still inline, false if the operation
         *   is running on a thread that is not the original caller
         */
        protected abstract boolean isInline();

        
Process the operation using the connector executor.
Returns:
true if the operation was accepted, false if the executor
    rejected execution/**
         * Process the operation using the connector executor.
         * @return true if the operation was accepted, false if the executor
         *     rejected execution
         */
        protected boolean process() {
            try {
                getEndpoint().getExecutor().execute(this);
                return true;
            } catch (RejectedExecutionException ree) {
                log.warn(sm.getString("endpoint.executor.fail", SocketWrapperBase.this) , ree);
            } catch (Throwable t) {
                ExceptionUtils.handleThrowable(t);
                // This means we got an OOM or similar creating a thread, or that
                // the pool and its queue are full
                log.error(sm.getString("endpoint.process.fail"), t);
            }
            return false;
        }

        
Start the operation, this will typically call run.
/**
         * Start the operation, this will typically call run.
         */
        protected void start() {
            run();
        }

        
End the operation.
/**
         * End the operation.
         */
        protected void end() {
        }

    }

    
Completion handler for vectored operations. This will check the completion of the operation,
then either continue or call the user provided completion handler.
/**
     * Completion handler for vectored operations. This will check the completion of the operation,
     * then either continue or call the user provided completion handler.
     */
    protected class VectoredIOCompletionHandler<A> implements CompletionHandler<Long, OperationState<A>> {
        @Override
        public void completed(Long nBytes, OperationState<A> state) {
            if (nBytes.longValue() < 0) {
                failed(new EOFException(), state);
            } else {
                state.nBytes += nBytes.longValue();
                CompletionState currentState = state.isInline() ? CompletionState.INLINE : CompletionState.DONE;
                boolean complete = true;
                boolean completion = true;
                if (state.check != null) {
                    CompletionHandlerCall call = state.check.callHandler(currentState, state.buffers, state.offset, state.length);
                    if (call == CompletionHandlerCall.CONTINUE) {
                        complete = false;
                    } else if (call == CompletionHandlerCall.NONE) {
                        completion = false;
                    }
                }
                if (complete) {
                    boolean notify = false;
                    state.semaphore.release();
                    if (state.read) {
                        readOperation = null;
                    } else {
                        writeOperation = null;
                    }
                    if (state.block == BlockingMode.BLOCK && currentState != CompletionState.INLINE) {
                        notify = true;
                    } else {
                        state.state = currentState;
                    }
                    state.end();
                    if (completion && state.handler != null) {
                        state.handler.completed(Long.valueOf(state.nBytes), state.attachment);
                    }
                    synchronized (state) {
                        state.completionDone = true;
                        if (notify) {
                            state.state = currentState;
                            state.notify();
                        }
                    }
                } else {
                    synchronized (state) {
                        state.completionDone = true;
                    }
                    state.run();
                }
            }
        }
        @Override
        public void failed(Throwable exc, OperationState<A> state) {
            IOException ioe = null;
            if (exc instanceof InterruptedByTimeoutException) {
                ioe = new SocketTimeoutException();
                exc = ioe;
            } else if (exc instanceof IOException) {
                ioe = (IOException) exc;
            }
            setError(ioe);
            boolean notify = false;
            state.semaphore.release();
            if (state.read) {
                readOperation = null;
            } else {
                writeOperation = null;
            }
            if (state.block == BlockingMode.BLOCK) {
                notify = true;
            } else {
                state.state = state.isInline() ? CompletionState.ERROR : CompletionState.DONE;
            }
            state.end();
            if (state.handler != null) {
                state.handler.failed(exc, state.attachment);
            }
            synchronized (state) {
                state.completionDone = true;
                if (notify) {
                    state.state = state.isInline() ? CompletionState.ERROR : CompletionState.DONE;
                    state.notify();
                }
            }
        }
    }

    
Allows using NIO2 style read/write.
Returns:
true if the connector has the capability enabled/**
     * Allows using NIO2 style read/write.
     *
     * @return {@code true} if the connector has the capability enabled
     */
    public boolean hasAsyncIO() {
        // The semaphores are only created if async IO is enabled
        return (readPending != null);
    }

    
Allows indicating if the connector needs semaphores.
Returns:
This default implementation always returns false/**
     * Allows indicating if the connector needs semaphores.
     *
     * @return This default implementation always returns {@code false}
     */
    public boolean needSemaphores() {
        return false;
    }

    
Allows indicating if the connector supports per operation timeout.
Returns:
This default implementation always returns false/**
     * Allows indicating if the connector supports per operation timeout.
     *
     * @return This default implementation always returns {@code false}
     */
    public boolean hasPerOperationTimeout() {
        return false;
    }

    
Allows checking if an asynchronous read operation is currently pending.
Returns:
true if the endpoint supports asynchronous IO and
 a read operation is being processed asynchronously/**
     * Allows checking if an asynchronous read operation is currently pending.
     * @return <code>true</code> if the endpoint supports asynchronous IO and
     *  a read operation is being processed asynchronously
     */
    public boolean isReadPending() {
        return false;
    }

    
Allows checking if an asynchronous write operation is currently pending.
Returns:
true if the endpoint supports asynchronous IO and
 a write operation is being processed asynchronously/**
     * Allows checking if an asynchronous write operation is currently pending.
     * @return <code>true</code> if the endpoint supports asynchronous IO and
     *  a write operation is being processed asynchronously
     */
    public boolean isWritePending() {
        return false;
    }

    
If an asynchronous read operation is pending, this method will block
until the operation completes, or the specified amount of time
has passed.
Params:
timeout – The maximum amount of time to wait
unit – The unit for the timeout
Returns:
true if the read operation is complete,
 false if the operation is still pending and
 the specified timeout has passed/**
     * If an asynchronous read operation is pending, this method will block
     * until the operation completes, or the specified amount of time
     * has passed.
     * @param timeout The maximum amount of time to wait
     * @param unit The unit for the timeout
     * @return <code>true</code> if the read operation is complete,
     *  <code>false</code> if the operation is still pending and
     *  the specified timeout has passed
     */
    @Deprecated
    public boolean awaitReadComplete(long timeout, TimeUnit unit) {
        return true;
    }

    
If an asynchronous write operation is pending, this method will block
until the operation completes, or the specified amount of time
has passed.
Params:
timeout – The maximum amount of time to wait
unit – The unit for the timeout
Returns:
true if the read operation is complete,
 false if the operation is still pending and
 the specified timeout has passed/**
     * If an asynchronous write operation is pending, this method will block
     * until the operation completes, or the specified amount of time
     * has passed.
     * @param timeout The maximum amount of time to wait
     * @param unit The unit for the timeout
     * @return <code>true</code> if the read operation is complete,
     *  <code>false</code> if the operation is still pending and
     *  the specified timeout has passed
     */
    @Deprecated
    public boolean awaitWriteComplete(long timeout, TimeUnit unit) {
        return true;
    }

    
Scatter read. The completion handler will be called once some
data has been read or an error occurred. The default NIO2
behavior is used: the completion handler will be called as soon
as some data has been read, even if the read has completed inline.
Params:
timeout – timeout duration for the read
unit – units for the timeout duration
attachment – an object to attach to the I/O operation that will be
       used when calling the completion handler
handler – to call when the IO is complete
dsts – buffers
Type parameters:
<A> – The attachment type
Returns:
the completion state (done, done inline, or still pending)/**
     * Scatter read. The completion handler will be called once some
     * data has been read or an error occurred. The default NIO2
     * behavior is used: the completion handler will be called as soon
     * as some data has been read, even if the read has completed inline.
     *
     * @param timeout timeout duration for the read
     * @param unit units for the timeout duration
     * @param attachment an object to attach to the I/O operation that will be
     *        used when calling the completion handler
     * @param handler to call when the IO is complete
     * @param dsts buffers
     * @param <A> The attachment type
     * @return the completion state (done, done inline, or still pending)
     */
    public final <A> CompletionState read(long timeout, TimeUnit unit, A attachment,
            CompletionHandler<Long, ? super A> handler, ByteBuffer... dsts) {
        if (dsts == null) {
            throw new IllegalArgumentException();
        }
        return read(dsts, 0, dsts.length, BlockingMode.CLASSIC, timeout, unit, attachment, null, handler);
    }

    
Scatter read. The completion handler will be called once some
data has been read or an error occurred. If a CompletionCheck
object has been provided, the completion handler will only be
called if the callHandler method returned true. If no
CompletionCheck object has been provided, the default NIO2
behavior is used: the completion handler will be called as soon
as some data has been read, even if the read has completed inline.
Params:
block – is the blocking mode that will be used for this operation
timeout – timeout duration for the read
unit – units for the timeout duration
attachment – an object to attach to the I/O operation that will be
       used when calling the completion handler
check – for the IO operation completion
handler – to call when the IO is complete
dsts – buffers
Type parameters:
<A> – The attachment type
Returns:
the completion state (done, done inline, or still pending)/**
     * Scatter read. The completion handler will be called once some
     * data has been read or an error occurred. If a CompletionCheck
     * object has been provided, the completion handler will only be
     * called if the callHandler method returned true. If no
     * CompletionCheck object has been provided, the default NIO2
     * behavior is used: the completion handler will be called as soon
     * as some data has been read, even if the read has completed inline.
     *
     * @param block is the blocking mode that will be used for this operation
     * @param timeout timeout duration for the read
     * @param unit units for the timeout duration
     * @param attachment an object to attach to the I/O operation that will be
     *        used when calling the completion handler
     * @param check for the IO operation completion
     * @param handler to call when the IO is complete
     * @param dsts buffers
     * @param <A> The attachment type
     * @return the completion state (done, done inline, or still pending)
     */
    public final <A> CompletionState read(BlockingMode block, long timeout,
            TimeUnit unit, A attachment, CompletionCheck check,
            CompletionHandler<Long, ? super A> handler, ByteBuffer... dsts) {
        if (dsts == null) {
            throw new IllegalArgumentException();
        }
        return read(dsts, 0, dsts.length, block, timeout, unit, attachment, check, handler);
    }

    
Scatter read. The completion handler will be called once some
data has been read or an error occurred. If a CompletionCheck
object has been provided, the completion handler will only be
called if the callHandler method returned true. If no
CompletionCheck object has been provided, the default NIO2
behavior is used: the completion handler will be called as soon
as some data has been read, even if the read has completed inline.
Params:
dsts – buffers
offset – in the buffer array
length – in the buffer array
block – is the blocking mode that will be used for this operation
timeout – timeout duration for the read
unit – units for the timeout duration
attachment – an object to attach to the I/O operation that will be
       used when calling the completion handler
check – for the IO operation completion
handler – to call when the IO is complete
Type parameters:
<A> – The attachment type
Returns:
the completion state (done, done inline, or still pending)/**
     * Scatter read. The completion handler will be called once some
     * data has been read or an error occurred. If a CompletionCheck
     * object has been provided, the completion handler will only be
     * called if the callHandler method returned true. If no
     * CompletionCheck object has been provided, the default NIO2
     * behavior is used: the completion handler will be called as soon
     * as some data has been read, even if the read has completed inline.
     *
     * @param dsts buffers
     * @param offset in the buffer array
     * @param length in the buffer array
     * @param block is the blocking mode that will be used for this operation
     * @param timeout timeout duration for the read
     * @param unit units for the timeout duration
     * @param attachment an object to attach to the I/O operation that will be
     *        used when calling the completion handler
     * @param check for the IO operation completion
     * @param handler to call when the IO is complete
     * @param <A> The attachment type
     * @return the completion state (done, done inline, or still pending)
     */
    public final <A> CompletionState read(ByteBuffer[] dsts, int offset, int length,
            BlockingMode block, long timeout, TimeUnit unit, A attachment,
            CompletionCheck check, CompletionHandler<Long, ? super A> handler) {
        return vectoredOperation(true, dsts, offset, length, block, timeout, unit, attachment, check, handler);
    }

    
Gather write. The completion handler will be called once some
data has been written or an error occurred. The default NIO2
behavior is used: the completion handler will be called, even
if the write is incomplete and data remains in the buffers, or
if the write completed inline.
Params:
timeout – timeout duration for the write
unit – units for the timeout duration
attachment – an object to attach to the I/O operation that will be
       used when calling the completion handler
handler – to call when the IO is complete
srcs – buffers
Type parameters:
<A> – The attachment type
Returns:
the completion state (done, done inline, or still pending)/**
     * Gather write. The completion handler will be called once some
     * data has been written or an error occurred. The default NIO2
     * behavior is used: the completion handler will be called, even
     * if the write is incomplete and data remains in the buffers, or
     * if the write completed inline.
     *
     * @param timeout timeout duration for the write
     * @param unit units for the timeout duration
     * @param attachment an object to attach to the I/O operation that will be
     *        used when calling the completion handler
     * @param handler to call when the IO is complete
     * @param srcs buffers
     * @param <A> The attachment type
     * @return the completion state (done, done inline, or still pending)
     */
    public final <A> CompletionState write(long timeout, TimeUnit unit, A attachment,
            CompletionHandler<Long, ? super A> handler, ByteBuffer... srcs) {
        if (srcs == null) {
            throw new IllegalArgumentException();
        }
        return write(srcs, 0, srcs.length, BlockingMode.CLASSIC, timeout, unit, attachment, null, handler);
    }

    
Gather write. The completion handler will be called once some
data has been written or an error occurred. If a CompletionCheck
object has been provided, the completion handler will only be
called if the callHandler method returned true. If no
CompletionCheck object has been provided, the default NIO2
behavior is used: the completion handler will be called, even
if the write is incomplete and data remains in the buffers, or
if the write completed inline.
Params:
block – is the blocking mode that will be used for this operation
timeout – timeout duration for the write
unit – units for the timeout duration
attachment – an object to attach to the I/O operation that will be
       used when calling the completion handler
check – for the IO operation completion
handler – to call when the IO is complete
srcs – buffers
Type parameters:
<A> – The attachment type
Returns:
the completion state (done, done inline, or still pending)/**
     * Gather write. The completion handler will be called once some
     * data has been written or an error occurred. If a CompletionCheck
     * object has been provided, the completion handler will only be
     * called if the callHandler method returned true. If no
     * CompletionCheck object has been provided, the default NIO2
     * behavior is used: the completion handler will be called, even
     * if the write is incomplete and data remains in the buffers, or
     * if the write completed inline.
     *
     * @param block is the blocking mode that will be used for this operation
     * @param timeout timeout duration for the write
     * @param unit units for the timeout duration
     * @param attachment an object to attach to the I/O operation that will be
     *        used when calling the completion handler
     * @param check for the IO operation completion
     * @param handler to call when the IO is complete
     * @param srcs buffers
     * @param <A> The attachment type
     * @return the completion state (done, done inline, or still pending)
     */
    public final <A> CompletionState write(BlockingMode block, long timeout,
            TimeUnit unit, A attachment, CompletionCheck check,
            CompletionHandler<Long, ? super A> handler, ByteBuffer... srcs) {
        if (srcs == null) {
            throw new IllegalArgumentException();
        }
        return write(srcs, 0, srcs.length, block, timeout, unit, attachment, check, handler);
    }

    
Gather write. The completion handler will be called once some
data has been written or an error occurred. If a CompletionCheck
object has been provided, the completion handler will only be
called if the callHandler method returned true. If no
CompletionCheck object has been provided, the default NIO2
behavior is used: the completion handler will be called, even
if the write is incomplete and data remains in the buffers, or
if the write completed inline.
Params:
srcs – buffers
offset – in the buffer array
length – in the buffer array
block – is the blocking mode that will be used for this operation
timeout – timeout duration for the write
unit – units for the timeout duration
attachment – an object to attach to the I/O operation that will be
       used when calling the completion handler
check – for the IO operation completion
handler – to call when the IO is complete
Type parameters:
<A> – The attachment type
Returns:
the completion state (done, done inline, or still pending)/**
     * Gather write. The completion handler will be called once some
     * data has been written or an error occurred. If a CompletionCheck
     * object has been provided, the completion handler will only be
     * called if the callHandler method returned true. If no
     * CompletionCheck object has been provided, the default NIO2
     * behavior is used: the completion handler will be called, even
     * if the write is incomplete and data remains in the buffers, or
     * if the write completed inline.
     *
     * @param srcs buffers
     * @param offset in the buffer array
     * @param length in the buffer array
     * @param block is the blocking mode that will be used for this operation
     * @param timeout timeout duration for the write
     * @param unit units for the timeout duration
     * @param attachment an object to attach to the I/O operation that will be
     *        used when calling the completion handler
     * @param check for the IO operation completion
     * @param handler to call when the IO is complete
     * @param <A> The attachment type
     * @return the completion state (done, done inline, or still pending)
     */
    public final <A> CompletionState write(ByteBuffer[] srcs, int offset, int length,
            BlockingMode block, long timeout, TimeUnit unit, A attachment,
            CompletionCheck check, CompletionHandler<Long, ? super A> handler) {
        return vectoredOperation(false, srcs, offset, length, block, timeout, unit, attachment, check, handler);
    }


    
Vectored operation. The completion handler will be called once
the operation is complete or an error occurred. If a CompletionCheck
object has been provided, the completion handler will only be
called if the callHandler method returned true. If no
CompletionCheck object has been provided, the default NIO2
behavior is used: the completion handler will be called, even
if the operation is incomplete, or if the operation completed inline.
Params:
read – true if the operation is a read, false if it is a write
buffers – buffers
offset – in the buffer array
length – in the buffer array
block – is the blocking mode that will be used for this operation
timeout – timeout duration for the write
unit – units for the timeout duration
attachment – an object to attach to the I/O operation that will be
       used when calling the completion handler
check – for the IO operation completion
handler – to call when the IO is complete
Type parameters:
<A> – The attachment type
Returns:
the completion state (done, done inline, or still pending)/**
     * Vectored operation. The completion handler will be called once
     * the operation is complete or an error occurred. If a CompletionCheck
     * object has been provided, the completion handler will only be
     * called if the callHandler method returned true. If no
     * CompletionCheck object has been provided, the default NIO2
     * behavior is used: the completion handler will be called, even
     * if the operation is incomplete, or if the operation completed inline.
     *
     * @param read true if the operation is a read, false if it is a write
     * @param buffers buffers
     * @param offset in the buffer array
     * @param length in the buffer array
     * @param block is the blocking mode that will be used for this operation
     * @param timeout timeout duration for the write
     * @param unit units for the timeout duration
     * @param attachment an object to attach to the I/O operation that will be
     *        used when calling the completion handler
     * @param check for the IO operation completion
     * @param handler to call when the IO is complete
     * @param <A> The attachment type
     * @return the completion state (done, done inline, or still pending)
     */
    protected final <A> CompletionState vectoredOperation(boolean read,
            ByteBuffer[] buffers, int offset, int length,
            BlockingMode block, long timeout, TimeUnit unit, A attachment,
            CompletionCheck check, CompletionHandler<Long, ? super A> handler) {
        IOException ioe = getError();
        if (ioe != null) {
            handler.failed(ioe, attachment);
            return CompletionState.ERROR;
        }
        if (timeout == -1) {
            timeout = AbstractEndpoint.toTimeout(read ? getReadTimeout() : getWriteTimeout());
            unit = TimeUnit.MILLISECONDS;
        } else if (!hasPerOperationTimeout() && (unit.toMillis(timeout) != (read ? getReadTimeout() : getWriteTimeout()))) {
            if (read) {
                setReadTimeout(unit.toMillis(timeout));
            } else {
                setWriteTimeout(unit.toMillis(timeout));
            }
        }
        if (block == BlockingMode.BLOCK || block == BlockingMode.SEMI_BLOCK) {
            try {
                if (read ? !readPending.tryAcquire(timeout, unit) : !writePending.tryAcquire(timeout, unit)) {
                    handler.failed(new SocketTimeoutException(), attachment);
                    return CompletionState.ERROR;
                }
            } catch (InterruptedException e) {
                handler.failed(e, attachment);
                return CompletionState.ERROR;
            }
        } else {
            if (read ? !readPending.tryAcquire() : !writePending.tryAcquire()) {
                if (block == BlockingMode.NON_BLOCK) {
                    return CompletionState.NOT_DONE;
                } else {
                    handler.failed(read ? new ReadPendingException() : new WritePendingException(), attachment);
                    return CompletionState.ERROR;
                }
            }
        }
        VectoredIOCompletionHandler<A> completion = new VectoredIOCompletionHandler<>();
        OperationState<A> state = newOperationState(read, buffers, offset, length, block, timeout, unit,
                attachment, check, handler, read ? readPending : writePending, completion);
        if (read) {
            readOperation = state;
        } else {
            writeOperation = state;
        }
        state.start();
        if (block == BlockingMode.BLOCK) {
            synchronized (state) {
                if (state.state == CompletionState.PENDING) {
                    try {
                        state.wait(unit.toMillis(timeout));
                        if (state.state == CompletionState.PENDING) {
                            return CompletionState.ERROR;
                        }
                    } catch (InterruptedException e) {
                        completion.failed(new SocketTimeoutException(), state);
                        return CompletionState.ERROR;
                    }
                }
            }
        }
        return state.state;
    }

    protected abstract <A> OperationState<A> newOperationState(boolean read,
            ByteBuffer[] buffers, int offset, int length,
            BlockingMode block, long timeout, TimeUnit unit, A attachment,
            CompletionCheck check, CompletionHandler<Long, ? super A> handler,
            Semaphore semaphore, VectoredIOCompletionHandler<A> completion);

    // --------------------------------------------------------- Utility methods

    protected static int transfer(byte[] from, int offset, int length, ByteBuffer to) {
        int max = Math.min(length, to.remaining());
        if (max > 0) {
            to.put(from, offset, max);
        }
        return max;
    }

    protected static int transfer(ByteBuffer from, ByteBuffer to) {
        int max = Math.min(from.remaining(), to.remaining());
        if (max > 0) {
            int fromLimit = from.limit();
            from.limit(from.position() + max);
            to.put(from);
            from.limit(fromLimit);
        }
        return max;
    }
}